Nokea
The second-messenger mechanism of hormone action operates by ________.
- A. synthesizing more of the hormone than is actually needed
- B. increasing the basal metabolic rate in the target organ
- C. not responding to a feedback mechanism
- D. binding to specific receptors and employing the services of G proteins and cAMP
Correct Answer: D
Rationale: The correct answer is D because the second-messenger mechanism involves the hormone binding to specific receptors on the cell surface, activating G proteins, which then trigger the production of cyclic adenosine monophosphate (cAMP) inside the cell. cAMP acts as a secondary messenger to relay the hormone's signal and initiate a cellular response. Synthesizing more hormone than needed (A) is not related to the mechanism. Increasing basal metabolic rate (B) is not a direct result of the second-messenger system. Not responding to feedback (C) contradicts the regulatory nature of hormone actions.
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All of the following are endocrine glands EXCEPT
- A. adrenal glands.
- B. sweat glands.
- C. parathyroid glands.
- D. pineal gland.
Correct Answer: B
Rationale: The correct answer is B: sweat glands. Endocrine glands secrete hormones directly into the bloodstream, affecting various organs and tissues. Sweat glands, on the other hand, are exocrine glands that release sweat through ducts onto the skin's surface to regulate body temperature. Adrenal glands produce hormones like cortisol and adrenaline (A), parathyroid glands regulate calcium levels in the body (C), and the pineal gland produces melatonin to regulate sleep-wake cycles (D). Therefore, sweat glands do not fit the definition of an endocrine gland, making them the correct choice.
Which of the following is the response to low plasma levels of calcium?
- A. Secretion of calcitonin
- B. Secretion of the beta cells of the islets of Langerhans
- C. Inhibition of the adenohypophyseal release of ACTH
- D. Secretion of PTH
Correct Answer: D
Rationale: The correct answer is D: Secretion of PTH. Low plasma levels of calcium trigger the parathyroid glands to release parathyroid hormone (PTH) to increase calcium levels. PTH acts on the bones to stimulate calcium release, on the kidneys to increase calcium reabsorption, and on the intestines to enhance absorption.
A: Secretion of calcitonin is incorrect because calcitonin is released in response to high calcium levels to lower them.
B: Secretion of the beta cells of the islets of Langerhans is incorrect as these cells secrete insulin in response to high blood glucose levels.
C: Inhibition of the adenohypophyseal release of ACTH is incorrect as ACTH is related to stress response, not calcium regulation.
An enlargement of the thyroid gland is the condition known as .
- A. acromegaly
- B. goiter
- C. parathyroidism
- D. Cushing's disease
Correct Answer: B
Rationale: The correct answer is B: goiter. An enlargement of the thyroid gland is specifically referred to as a goiter. This condition can be caused by iodine deficiency or other factors affecting thyroid hormone production. Acromegaly (A) is a disorder caused by excessive growth hormone, unrelated to the thyroid. Parathyroidism (C) refers to issues with the parathyroid glands, not the thyroid. Cushing's disease (D) is a condition involving excessive cortisol production, not thyroid enlargement. Therefore, the correct term for an enlarged thyroid gland is goiter.
Calcitonin is a hormone of which of following:
- A. Adrenal cortex.
- B. Thyroid gland.
- C. Pituitary gland.
- D. Thymus gland.
Correct Answer: B
Rationale: Calcitonin is a hormone produced by the thyroid gland. It helps regulate calcium levels in the body by inhibiting bone breakdown and lowering blood calcium levels. The thyroid gland is responsible for producing various hormones, including calcitonin. Adrenal cortex (A) produces hormones like cortisol, Pituitary gland (C) produces hormones like growth hormone, and Thymus gland (D) is involved in immune function, not hormone regulation. Therefore, the correct answer is B (Thyroid gland).
The secretion of cortisol by the adrenal gland suppresses further secretion of ACTH by the anterior pituitary gland. What is this interaction called?
- A. Cerebral lateralization
- B. Circadian rhythm
- C. Cellular differentiation
- D. Negative feedback control
Correct Answer: D
Rationale: The correct answer is D: Negative feedback control. This interaction is a classic example of negative feedback control in the endocrine system. Cortisol inhibits the release of ACTH, which in turn reduces the stimulation of cortisol production, creating a feedback loop to maintain hormonal balance. Choice A, cerebral lateralization, refers to the specialization of brain function. Choice B, circadian rhythm, pertains to the 24-hour biological cycle. Choice C, cellular differentiation, involves the process of cells becoming specialized for specific functions. Thus, the correct answer is D because it accurately describes the feedback mechanism at play in the cortisol-ACTH interaction.